Bobbin case for a sewing machine

ABSTRACT

A bobbin case is used in a sewing machine for mounting a bobbin, and includes a case body having a base wall, a case shaft extending along a central line from the base wall for rotatably mounting the bobbin, and a rim having entry and exit holes to define a tensioning path therebetween, and a diverting concaivity configured to divert a running route which is disposed downstream of the tensioning path. A lead-out member is disposed downstream of the running route. A leaf spring is positioned on the rim, and is configured to guide an under thread of the bobbin to run along the tensioning path with an urging force, and continued on running along the running route to the lead-out member to be interlocked with an upper thread for a sewing action.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a sewing machine, more particularly to a bobbin case used in a sewing machine for mounting a bobbin that supplies an under thread.

2. Description of the Related Art

A sewing machine generally has a rotary shuttle device which is disposed under a needle plate for supplying an under thread, and which includes a hook driven to rotate about a horizontal axis, a bobbin case holder housed in the hook, and a bobbin case detachably attached to the bobbin case holder for receiving a bobbin on which the under thread is wound. During a sewing operation, the hook is rotated relative to the bobbin case holder, and the under thread is pulled out and supplied through the bobbin case to a lower portion of a piece of cloth to be sewn. The bobbin case is provided to guide the under thread pulled out of the bobbin upward for interlocking with an upper thread supplied from a needle above the needle plate.

Referring to FIGS. 1 and 2, a conventional bobbin case is shown to include a case body 1 and a leaf spring 2. The case body 1 has a base wall 101, a shaft 103 extending from the base wall 101 along a central line that is in line with a horizontal axis of a hook of a rotary shuttle device when the bobbin case is received in a bobbin case holder, and a peripheral wall 102 extending from an annular marginal region of the base wall 101 in a direction of the central line and configured to open at a top 106. The peripheral wall 102 has an inclined slit 104 extending therethrough to permit an under thread 301 of a bobbin 3 to be led out through the peripheral wall 102. The under thread 301 is held between the leaf spring 2 and the peripheral wall 102 in a tensed state, is guided by a guiding end 201 of the leaf spring 2 that is engaged in an exit hole 105 in the peripheral wall 102, and runs through a lead-out member 107.

Referring to FIG. 3, during a sewing operation, the under thread 301 is liable to slip off the guiding end 201 and toward the base wall 101 so that the tension force applied to the under thread 301 is insufficient, thereby adversely affecting sewing quality.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a bobbin case which can ensure that an under thread of a bobbin received therein is held in a tensed state.

According to this invention, the bobbin case includes a case body having a base wall which defines an annular marginal region that surrounds a central line, and which has a portion cut out so as to form an offset surface that is offset from the central line, a case shaft which extends from the base wall along the central line, and which is configured to permit a bobbin to be rotatably sleeved thereon so as to reel off an under thread to be led outwardly of the annular marginal region, and front and rear rim segments which extend from the annular marginal region in a direction of the central line, and which are interconnected by the offset surface. The front rim segment extends angularly to terminate at a longitudinally extending edge, and has entry and exit holes which are angularly displaced from each other to define a tensioning path therebetween, and a diverting concavity which extends from the longitudinally extending edge angularly and toward the exit hole, and which is configured to divert a running route which is disposed downstream of the tensioning path, inwardly of the annular marginal region. A lead-out member is disposed on the offset surface and downstream of the diverting concavity for further leading the under thread toward a needle plate. A leaf spring has a positioned segment disposed to be fastened to the front rim segment, and an urging segment which extends lengthwise from the positioned segment to terminate at a guiding end that is engaged in the exit hole, and that is configured to guide the under thread to run along the running route to the lead-out member through the diverting concavity. The urging segment is provided with an urging force such that the under thread led out of the entry hole to run along the tensioning path is subject to the urging force so as to be placed in a tensed state when the under thread exits the guiding end for continuing on running along the running route.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiment of the invention, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a conventional bobbin case and a bobbin;

FIG. 2 is a perspective view of the conventional bobbin case in which the bobbin is mounted;

FIG. 3 is a perspective view of the conventional bobbin case when an under thread of the bobbin is slipped off;

FIG. 4 is a perspective view of the preferred embodiment of a bobbin case according to this invention, and a bobbin;

FIG. 5 is a side view of the preferred embodiment; and

FIG. 6 is a perspective view of the preferred embodiment in which the bobbin is mounted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 4 to 6, the preferred embodiment of a bobbin case according to the present invention is shown to comprise a case body 10, a lead-out member 16, and a leaf spring 20.

The case body 10 has a base wall 11 which defines an annular marginal region 111 that surrounds a central line (X) that is in line with a horizontal axis of a hook (not shown) when received in the hook, and which has a portion cut out so as to form an offset surface 112 that is offset from the central line (X), a case shaft 14 which extends from the base wall 11 along the central line (X), and which is configured to permit a bobbin 100 to be rotatably sleeved thereon so as to reel off an under thread 110 to be led outwardly of the annular marginal region 111, and a rim 12 extending from the annular marginal region 111 in a direction of the central line (X) to terminate at a circumferentially extending edge 121. The rim 12 includes front and rear rim segments (12 a, 12 b) which are interconnected by the offset surface 112. The front rim segment (12 a) extends angularly to terminate at a longitudinally extending edge 15, and has outer and inner surface regions 13, 18 radially opposite to each other. The outer surface region 13 has an inclined slit 122 which extends through the inner surface region 18 and which communicates the circumferentially extending edge 121 with an entry hole 124 so as to permit the under thread 110 to be guided through the inclined slit 122 into the entry hole 124. An exit hole 123 is angularly displaced from the entry hole 124 to define a tensioning path (P) therebetween. A diverting concavity 17 extends from the longitudinally extending edge 15 angularly and toward the exit hole 123, and has a diverting surface 171 which is disposed to face the circumferentially extending edge 121 and which is inclined gradually from the outer surface region 13 to the inner surface region 18. Thus, the diverting surface 171 can divert a running route (R) which is disposed downstream of the tensioning path (P), inwardly of the annular marginal region 111.

The lead-out member 16 is disposed on the offset surface 112 and downstream of the diverting concavity 17 for further leading the under thread 110 toward a needle plate (not shown) of a sewing machine. In this embodiment, the lead-out member 16 is in the form of a coil which defines a through passage 161 for passage of the under thread 110.

The leaf spring 20 has a positioned segment 22 disposed to be fastened to the front rim segment (12 a), and an urging segment 23 which extends lengthwise from the positioned segment 22 to terminate at a guiding end 21 that is engaged in the exit hole 123, and that is bent to forma bearing surface 211 facing the circumferentially extending edge 121 so as to guide the under thread 110 to run along the running route (R) to the lead-out member 16 through the diverting concavity 17. The urging segment 23 is provided with an urging force such that the under thread 110 led out of the entry hole 124 to run along the tensioning path (P) is subject to the urging force so as to be placed in a tensed state when the under thread 110 exits the guiding end 21 for continuing on running along the running route (R).

As illustrated, with provision of the diverting concavity 17 that can divert the running route (R) downstream of the tensioning path (P) and inwardly of the annular marginal region 111, when performing a sewing operation, the under thread 110 can run along the running route (R) while being subject to the urging force to be placed in the tensed state. Slippage of the under thread 110 off the guiding end 21 can be avoided, thereby ensuring the under thread 110 to be in a steady, tensed state during the sewing operation.

While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this invention is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretations and equivalent arrangements. 

1. A bobbin case adapted to be used in a sewing machine for mounting a bobbin which is disposed under a needle plate to supply an under thread, the bobbin case comprising: a case body having a base wall which defines an annular marginal region that surrounds a central line, and which has a portion cut out so as to form an offset surface that is offset from the central line, a case shaft which extends from said base wall along the central line, and which is configured to permit the bobbin to be rotatably sleeved thereon so as to reel off the under thread to be led outwardly of said annular marginal region, and front and rear rim segments which extend from said annular marginal region in a direction of the central line, and which are interconnected by said offset surface, said front rim segment extending angularly to terminate at a longitudinally extending edge, and having entry and exit holes which are angularly displaced from each other to define a tensioning path therebetween, and a diverting concavity which extends from said longitudinally extending edge angularly and toward said exit hole, and which is configured to divert a running route which is disposed downstream of the tensioning path, inwardly of said annular marginal region; a lead-out member disposed on said offset surface and downstream of said diverting concavity for further leading the under thread toward the needle plate; and a leaf spring which has a positioned segment disposed to be fastened to said front rim segment, and an urging segment which extends lengthwise from said positioned segment to terminate at a guiding end that is engaged in said exit hole, and that is configured to guide the under thread to run along the running route to said lead-out member through said diverting concavity, said urging segment being provided with an urging force such that the under thread led out of said entry hole to run along the tensioning path is subject to the urging force so as to be placed in a tensed state when the under thread exits said guiding end for continuing on running along the running route.
 2. The bobbin case according to claim 1, wherein said front rim segment extends in the direction of the central line to terminate at a circumferentially extending edge, and has outer and inner surface regions radially opposite to each other, said outer surface region having an inclined slit which extends through said inner surface region and which communicates said circumferentially extending edge with said entry hole so as to permit the under thread to be guided through said inclined slit into said entry hole.
 3. The bobbin case according to claim 2, wherein said guiding end is integrally formed with said urging segment and is bent to form a bearing surface facing said circumferentially extending edge.
 4. The bobbin case according to claim 3, wherein said diverting concavity has a diverting surface which is disposed to face said circumferentially extending edge and which is inclined gradually from said outer surface region to said inner surface region.
 5. The bobbin case according to claim 1, wherein said lead-out member is in form of a coil which defines a through passage for passage of the under thread. 